Method of making an electronic device using an uniaxial conductive adhesive

ABSTRACT

An electronic device made by the method of connecting a circuit member (18) to a substrate (12) wherein the method includes the steps of applying an adhesive (22) including a resin having a twenty to twenty-five percent by weight content of conductive metal particles over the mounting surface (14) of the substrate (12) wherein the resin is a dielectric preventing conductivity between the spaced metal particles therein and mounting the circuit member (18) on the adhesive (22) while vertically aligning conductive terminals (20) of the circuit member (18) over preselected ones of conductive paths (16) of the substrate (12). The percent by weight content of the conductive metal particles in the adhesive (22) is concentrated between each conductive terminal (20) and the vertically aligned conductive paths (16) to between forty to fifty percent by weight to decrease the spacing between the metal particles allowing conductivity through the resin and making the resin uniaxially conductive vertically between the conductive terminal (20) and conductive bath (16).

TECHNICAL FIELD

The subject invention relates to an electronic device and anelectrically conductive adhesive therefor. The invention further relatesto a method of connecting a circuit member having a plurality oflaterally spaced conductive terminals to a substrate including a surfacehaving a plurality of laterally spaced conductive paths utilizing theadhesive.

BACKGROUND ART

In many electrical applications, it is desirable to connect anelectrical component having a plurality of conductive terminals to asubstrate including a plurality of laterally spaced conductive pathssuch that the conductive terminals are aligned with the conductive pathsin a predetermined pattern. For proper function, current is passed fromthe aligned conductive terminal to the substrate path, or visa a versa.It is undesirable for current to pass between laterally spaced terminalsor conductive pad, such conductivity causing shorting of the circuit.This desired function is referred to as uniaxial conductivity.

Conventional methods of connecting the conductive terminals to thesubstrate generally include soldering techniques. Soldering requires dotdeposition; that is, application of the solder only on the terminals andnot therebetween. Soldering further requires specific temperatureresistant components and substrates. Such materials must withstand the400° F. and greater temperatures generally encountered in the solderapplication.

The U.S. Pat. No. 4,113,981 to Fujita et al, issued Sept. 12, 1978,discloses an electrically conductive adhesive for connecting arrays ofconductors. The adhesive includes a nonconductive base and electricallyconductive particles incorporated into the base. The patent requiresthat the particles are not in contact with one another. The adhesiveprovides conductivity in one direction between two facing members butdoes not provide electric conductivity in the lateral direction. TheFujita et al patent requires a mixing ratio of between thirty to sixtypercent by volume of conductive particles in the adhesive base. When theproportion of the conductive particles is less than thirty percent byvolume, the value of the electrical resistance in the lateral directionbegins to be lowered and, when the amount of conductive particles isabout sixty percent by volume, a substantial conductivity is manifestedin the lateral direction. The patent states that it is preferred thatthe mixing ratio of the conductive particles be lower than about thirtypercent by volume. Additionally, the patent states that the mixing ratiois determined within the above range so that at least one electricallyconductive particle is present between opposed facing members to beelectrically connected with each other. In practice, such metalparticles are chosen to be within the range of approximately 8 to 10microns. This method therefor requires that the terminal members bebrought to within 8 to 10 microns of the substrate paths in order toprovide for connection between the terminal member, the electricalparticle, and the conductive paths. Such practice requires clean roomtechniques because in such a microscopic size range, dust particlecontamination must be prevented. Therefore, the Fujita et al patent isdependent upon the concept that the space in between the conductiveelements must be the same size as the largest of the conductiveparticles in the adhesive and that the conductive particles in theadhesive must be substantially the same size and shape. Consequently,there is a need for a uniaxially conductive adhesive not requiring theclose tolerances or clean room limitations of prior art adhesives.

It has been reported that the conductivity of an adhesive resin having aconductive metal mixed therein is dependent upon the concentration ofthe adhesive. Polymer Science Technology, Vol. 15, Plenum Press (1981).The instant invention applies this concept to derive a uniaxialconductive adhesive.

STATEMENT OF THE INVENTION

According to the present invention, there is provided a method ofconnecting an electronic circuit member having a plurality of laterallyspaced electrically conductive terminals to a substrate including asurface having a plurality of laterally spaced conductive paths, themethod including the steps of applying an adhesive including a resinhaving a twenty to twenty-five percent by weight content of conductivemetal particles over the surface of the substrate having the conductivepaths, the resin being a dielectric preventing conductivity between thespaced metal particles in the adhesive, and mounting the circuit memberon the adhesive while vertically aligning the conductive terminals overpreselected ones of the conductive paths. The invention is characterizedby the step of concentrating the percent by weight content of theconductive metal particles in the adhesive between each conductiveterminal and the vertically aligned conductive path to between forty tofifty percent by weight to decrease the spacing between the metalparticles allowing conductivity through the resin and making the resinconductive vertically between the conductive terminals and paths whilethe adhesive resin in the unconcentrated adhesive remains nonconductivebetween laterally spaced terminals and conductive paths.

The instant invention further provides an electric device including thesubstrate, the circuit member, and the adhesive disposed over themounting surface of the substrate. The adhesive includes the dielectrica resin having about forty to fifty percent by weight conductive metalparticles between the vertically aligned terminals and the conductivepaths and is uniaxially conductive vertically therebetween. The resinincludes twenty to twenty-five percent by weight conductive metalbetween laterally spaced terminals and conductive paths and the resin isnonconductive laterally therebetween.

FIGURES IN THE DRAWINGS

Other advantages of the present invention will be readily appreciated asthe same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a plan view of a circuit member mounted upon a substrate;

FIG. 2 is a cross sectional view taken substantially along lines 2--2 ofFIG. 1;

FIG. 3 is cross sectional view of the circuit member mounted on asubstrate and means for applying pressure to the circuit member againstthe substrate;

FIG. 4 is a graph of current versus voltage showing insulationresistance of the subject adhesive between laterally spaced terminals;

FIG. 5 is a graph of current versus voltage showing conductivity betweenaligned terminal members and conductive substrate paths and;

FIG. 6 is an enlarged view of the connection between the conductiveterminal and the conductive path by the subject adhesive.

DETAILED DESCRIPTION OF THE DRAWINGS

An electrical device constructed in accordance with the instantinvention is generally shown at 10 in FIGS. 1-3. The device includes asubstrate is generally indicated at 12. The substrate is a supportingmaterial on or in which parts of a circuit are attached or made. Asubstrate may be passive or active.

The substrate includes a mounting surface 14 having a plurality oflaterally spaced conductive paths 16 thereon. Such a substrate isgenerally referred to as printed circuit in which normally foundinterconnecting wires are replaced by conductive strips 16 printed,etched, or otherwise mounted onto the insulating substrate 12. In otherwords, the substrate is nonconductive, providing insulation between theconductive paths 16. The substrate 12 may also be referred to as printedcircuit board or insulating board onto which the conductive paths 16 orcircuit are printed.

A circuit member is generally indicated at 18. The circuit member 18 maybe in the form of any one of various types of electrical components,such as capacitors, resistors etc. or may be in the form of othersemiconductors. Alternatively, circuit member 18 may be a secondsubstrate mounted upon a first substrate 12.

The circuit member 18 includes a plurality of laterally spacedconductive terminals 20 aligned vertically over selected ones of theconductive paths 16. Functionally it is desirable to have uniaxialelectrical conductivity to or from the conductive paths 16 to theconductive terminals 20, without electrical conductivity betweenlaterally spaced conductive paths 16 or conductive terminals 20.

An adhesive coating 22 is disposed over the mounting surface 14 foradhering the circuit member 18 to the substrate 12. The adhesive 22includes a resin having about forty to fifty percent by weightconductive metal between the vertically aligned terminals 20 andconductive paths 16 and the resin is conductive vertically or uniaxiallytherebetween. The adhesive 22 includes about twenty to twenty-fivepercent by weight conductive metal between laterally spaced terminals 20or conductive paths 16 and the resin is therefore nonconductivelaterally therebetween. The lower percentage of metal filler in theadhesive 22 is not sufficient to support electrical current flow throughthe resin.

The adhesive 22 includes conductive metal particles in powder form orthe alloy of the conductive metal particles in powder form. Conductivemetals may be selected from the group including nickel, silver,graphite, palladium, platium, gold, chromium, aluminum, cadmium, cobalt,copper, iron, indium, iridium, magnesium, molybdenum, tin, tungsten,zinc, gallium, germanium, and antimony and other conductive materials.The metal powder may have a size of 0.8 microns to 40 microns.Preferably, the metal powder includes particles having an average sizeof 0.8 to 7 microns. Said another way, in the preferred range thelargest particle may be at least eight (8) times larger than thesmallest with an array of different sizes therebetween. The size of theparticles may be determined by the size of the components adheredtogether, larger components can be spaced further apart thereby allowingfor larger size particles to be used.

The adhesive further includes a polymerized resin in its pure form or asa mixture of several types of resins. The resin may be selected from thegroup including epoxy resins and modified resins with hardeners such asepoxy novalac resins, acrylic resins and modified acrylic resins such asmethylacrylic resin or n-butyl acrylic resin, polyester resins andmodified thereof such as polyaclylates and polybutylene terephthalate,silicone resins such as methyl trimethoxysilane and ethylorthosilicate,phenoxy resins, polyurethane resins, polysulfide, cyanoacrylates,UV-curable polymers, and other well known adhesive resins. The resinsare generally considered nonconductive in the polymerized state.However, pursuant to the subject invention, the resin is made conductiveby the step of concentrating the metal powder mixed therein to betweenforty to fifty percent by weight.

The resin is a dielectric preventing conductivity between spaced metalparticles therein. As shown in FIG. 6, the percent by weight content ofthe metal particles in the resin is concentrated between the conductiveterminals 20 and conductive paths 16 thereby decreasing the spacingbetween the metal particles. The decreased spacing allows conductivitythrough the resin providing conductivity between the aligned conductiveterminals 20 and conductive paths 16. The metal particles suspended inthe resin between laterally sapced conductive terminals 20 andconductive paths 16 are not concentrated. The resin preventsconductivity between spaced metal particles. The effect achieved isuniaxial conductivity between aligned conductive members 16,20 andinsulation or nonconductivity therebetweeen.

The terminal members 20 may be substantially rigid pins 20 extendinglaterally from the circuit member 18. Preferably, the distance betweenthe conductive terminals 20 and the mounting surface 14 is less than orequal to 20 microns. However, the terminal members 20 are often notcoplanar as they extend from a circuit member 18. Hence, the distancebetween the terminal members 20 and the mounting surface 14 of thesubstrate 12 may vary. The terminal members 20 may take other forms andhardness. The example, the terminal members 20 may be flexible foilprojection extending from the circuit member 18. Alternatively, theterminal members 20 may be rigid members mounted directly on the body ofthe circuit member 18.

The instant invention includes a method of connecting the circuit member18 having the plurality of laterally spaced conductive terminals 20 tothe substrate 12 which having the mounting surface 14 presenting theplurality of laterally spaced conductive paths 16 thereon. The methodincludes the steps of applying the adhesive 22 including the resinhaving a twenty to twenty-five percent by weight content of theconductive metal particles over the mounting surface 14 of the substrate12 having the conductive paths 16. Preferably, the adhesive is appliedin a layer greater than 20 microns over the entire surface, i.e., theconductive and nonconductive portions to an even upper surface.Alternatively, the adhesive may be applied in an amount so as to securethe circuit member 18 to the substrate or in an amount covering allelectrical components and thereby providing an effective environmentalseal.

The circuit member 18 is mounted on the adhesive 22 while verticallyaligning the conductive terminals 20 over preselected ones of theconductive paths 16. The method is characterized by the step ofconcentrating the percent by weight content of the conductive metalparticles in the adhesive 22 between each conductive terminal 20 and thevertically aligned conductive paths 16 to between forty to fifty percentby weight to decrease the spacing between the metal particles and makethe resin conductive vertically therebetween while the resin in theunconcentrated adhesive remains nonconductive between laterally spacedterminals 20 and conductive paths 16. In other words, if the metal inthe cured adhesive 22 between the conductive terminals 20 and theconductive paths 16 is increased or concentrated from between twenty andtwenty-five percent to between forty and fifty percent by weight, thereis conductivity in these concentrated regions and no conductivity in theunconcentrated regions therebetween. Hence, the instant methodaffectively provides a uniaxially conductive adhesive which isconductive between aligned conductive terminals 20 and conductive paths16 but is nonconductive between laterally spaced terminals 20 andconductive paths 16.

The concentration of metal in the adhesive may be concentrated byapplying pressure between the terminal 20 and the vertically alignedconductive path 16 to concentrate the conductive metal therebetween.Such application of pressure effective forces nonplanar terminal memberin coplanarity. As illustrated in FIG. 3, a pressure applying member 24can be used to apply pressure against the circuit member 18 therebyeffectively applying pressure between the terminal member 20 andconductive path 16 as the two are moved together. Such pressureconcentrates the metal in the adhesive 22 between the conductive paths16 and terminal member 20 while not concentrating the adhesive betweenlaterally spaced terminals 20 and conductive path 16. When the terminalmembers 20 are substantially rigid pins 20 extending from the circuitmember 18, the concentrating step may be defined as applying pressure onthe circuit member 18 against the substrate 12. Preferably, pressure maybe applied from three to forty pounds per square inch dependent upon thesize of the circuit member 18 and/or terminal sizes. The conductiveterminal 20 is preferably moved to within 20 microns or less of thesubstrate 14. Each of these preferred values may vary as the terminalmembers are generally not coplanar as they extend from the circuitmember 18. Hence, the adhesive 22 must be concentrated into thepreferred range of forty to fifty percent metal content at each terminalmember 20 for complete conductivity. If the terminal members 20 areflexible, the pressure need be applied directly to the terminal members20.

The adhesive 22 is cured at a predetermined time and temperature as thepressure is applied, i.e., a holding force maintains each terminalmember 20 in predetermined closely spaced relationship to its associatedconductive path 16. Generally, the adhesive 22 may be cured at roomtemperature to 250° C. for a period of a few seconds to one hour, thesevalues being dependent upon the adhesive used.

When the adhesive 22 is an ultraviolet curable adhesive, the curing stepis accomplished by irradiating the adhesive 22 under an ultraviolet lampfor a predetermined amount of time.

Although the pressure may be varied dependent upon the size of thecircuit member 18 being used, preferably, ounces to ten pounds ofpressure per square inch is applied dependent upon the size of thecomponent and/or structural characteristics of the terminals.

Initially, the adhesive 22 is prepared by mixing an adhesive resin and ametal powder together uniformly to suspend the metal powder within theadhesive. The adhesive is brought to a preferred viscosity, preferablybetween the range of 10,000 to 40,000 CPS. Most preferably, theviscosity of the adhesive mixture is between 15,000 to 20,000 CPS. Theviscosity values may be varied dependent upon the nature of the metalpowder, the viscosity determining the ability of the adhesive 22 tosuspend the metal in a uniform mixture.

The instant invention provides an adhesive 22 for connecting the circuitmember 18 having the plurality of laterally spaced conductive terminals20 to the substrate 12 including the mounting surface 14 having theplurality of laterally spaced conductive paths 16. The adhesive 22includes a mixture of the polymeric resin and twenty to twenty-fivepercent by weight of a pure conductive metal powder or alloy thereofuniformly suspended in the resin as a resin/metal suspension. Theadhesive 22 is characterized by the resin being nonconductive as theresin/metal suspension and the resin being conductive when concentratedto included forty to fifty percent by weight of the metal.

The subject adhesive can be used in a variety of environments. Theadhesive can be characterized as a metal to metal adhesive for bonding aconductive terminal to a conductive path on a substrate. In addition,the adhesive can adhere a circuit member to a substrate board. Withelectronic assemblies, the adhesive can be used to adhere components tosubstrates whereby component terminations are electrically connected tosubstrate conductive paths such as printed wiring thereby replacing allsoldering techniques. The adhesive can be used in surface mounttechnology, with printed wiring boards or printed circuit boards.Additionally, the adhesive may be used in conventional through holetechniques, hybrid technology, flip chip or chip on board technology,with tape automated bonding or pin grid arrays wherein chips (integratedcircuits) are adhered to arrays and arrays to printed wiring boards.

The adhesive can also be used to replace omnidirectional conductiveadhesives which previously have required insulative material betweenconductors. The adhesive can be used for substrate to substrateattachment such as with flexible printed wiring boards to rigid wiringboards, flexible wiring boards to flexible wiring boards and rigidprinted wiring boards to rigid wiring boards, etc. The adhesive can beuse with cable (wire) to substrate attachments, such as with flatflexible cable, flat ribbon cable, round wire cable and other forms ofcable. The adhesive may be used in connector applications to improvereliability wherein wire cable is connected to other attachments such asinsulation displacement connectors sealing, connector to connectorattachment and sealing, and connector to printed circuit boards.

Another area where the adhesive may be used is with componentfabrication. Examples of such uses are with semiconductors to lead frame(conductor) attachments such as integrated circuits, transistors anddiodes. Lid sealing of certain integrated circuits can also beaccomplished. The adhesive replaces other bonding techniques such asthermal compression, ultrasonic compression and other methods previouslybeing used. Passive elements such as capacitors and resistors may alsobe connected to leads.

The subject adhesive can be used in electromagnets interference (EMI)and radio frequency interference (EFI) sealing techniques such as lidsealing.

The subject adhesive further provides utility in the repair of substrateconductor traces.

In general, the subject adhesive may be used as a general adhesive forelectrical device connection to various other devices.

The instant invention provides several significant advantages over priorart adhesives. As the subject adhesive may be cured at room temperatureor at least at lower temperatures than prior art soldering techniques,various substrate materials heretofore not usable can be utilized.Nonceramic substrates which need not withstand the high temperatureenvironment of solder may be utilized thereby lowering the expense ofcompleted circuits.

The subject adhesive further provides a coating over the component partseffecting an environmental seal.

Soldering, is a specific method, providing specific problems. Theapplication of solder only bonds where the solder was applied and wasconductive at those points. The instant invention provides an adhesivematerial for the entire substrate surface as well as over componentsmounted thereon, yet provides conductivity only where desired. Theinstant invention further eliminates the cleaning required in prior artsoldering techniques. Such cleaning requires the exposure of the circuitboard to harsh chemicals not required by the instant invention. Soldermask can also eliminated.

The instant invention does not exhibit migration or electrolysis foundin prior art techniques. The instant invention further eliminatescoatings on copper printed circuits previously required such as tinplating or seal bright.

In general, an advantage of the instant invention is that the adhesiveno longer becomes a limiting factor in choosing substrates.Additionally, uniaxial conductivity can be obtained with extremely closelateral spacing of conductors.

A first embodiment of the inventor was made to include mixture of 10grams of EPIC R1003, modified epoxy resin, sold by Epic Resins, adivision of RTE Corporation, 1900 East North Street, Waukesh, Wis.53186, and 5 grams of EPIC H5002 modified aliphatic amine (epoxy resinhardener), also sold by Epic Resins, added at room temperature to 3.75grams of 99.8% nickel powder, 0.8 u as measured by Fisher subsieve, soldby Aldrich Chemical Co., 940 West Saint Paul Ave., Milwaukee, Wis.53133. The chemicals are mixed well until a uniform mixture is obtained.The viscosity of the mixture was about 15,000 cps, so that the epoxyresin held the nickel powder in suspension.

The epoxy resin and nickel powder mixture was uniformly coated on a PCboard (made by 3M, vapor phase, reflow solding fluorinet liquidsFC-70/FC-71), at a thickness of 80 um. A digital (integrated circuit),(M1511D5 with 14 pins), was placed on the glue coated PC board. Thedigital integrated circuit's pins were correspondingly matched to themetal strips on the PC board. The spacing between substrate conductivepaths was 500 um. About 4 pounds of pressure was placed on the digitalintegrated circuit for 15 minutes and at 150° C. in order to completecure.

After cure, conductivity between pins (laterally) was greater then ohms10¹³ (not conductive) yet the conductivity between pins andcorresponding metal strips on the PC board was 10⁻³ ohms (excellentconductivity).

A second embodiment of the invention was made wherein 10 grams of EpicS7020A, from Epic Resins, epoxy resin diglycidyl ether of bisphenol A, 5grams Epic S7020B, from Epic Resins, modified amine, and 3.75 gramsnickel powder, INCO type 123, 3-7 um, sold by The International NickelCompany, Inc. were mixed to a uniform suspension having a viscositybetween 20,000 to 22,000 cps. A digital integrated circuit was mountedon a PC board as in the first embodiment of the invention. A pressure of4 pounds was applied to the circuits and curing was effected at atemperature of 130° C. for 15 minutes. Excellent vertical conductivitywas obtained with effectively no lateral conductivity.

A third example of the invention includes 10 grams of Norbak 179-60,which is a single component, solvent-free epoxy resin, sold by RexnordChemical Products, Inc., Resin, Systems, 6120 E 58th Avenue, CommerceCity, CO, mixed with 2 grams of INCO type 123 Nickel powder, size 3-7 umand 0.5 gram of No. 4739 graphite, 5 um powder, sold by SuperiorGraphite Co., 120 South Riverside Place, Chicago, Ill. 60606, to auniform suspension having a viscosity of 20,000-25,000 cps. A digitalintegrated circuit was mounted on a PC board as in the first embodimentpreviously discussed. A pressure of 4 pounds was applied to the circuitand curing was effected at a temperature of 150° C. 15 minutes.Conductivity and insulation resistance are shown graphically in FIGS. 4and 5.

FIG. 4 illustrates insulating resistance of the adhesive laterallybetween terminals over a range of voltage (forward and reversepolarity). No breakdown of insulation occurred over the tested voltagerange.

FIG. 5 illustrates conductivity between the terminal pins and conductivemetal of the PC board. Beyond the threshold voltage, current wasconducted and constant over the tested voltage range.

In combination, FIGS. 4 and 5 show good uniaxial conductivity in thevertical direction with effective insulation in the lateral directionover a wide test range.

Another embodiment of the invention includes 5 grams EJN-002, UVdielectric coating, sold by Polytronix Inc., P.O. Box 3024, Richardson,Tx. 75080 mixed with 1 gram silver powder 2.0-3.5 um, sold by AlfaProduct, Thiako/Ventron Division, P.O. Box 299, 152 Andover Street,Danvers, Mass. 01923.

0.3 grams 5 um graphite powder, No. 4739, Superior Graphite Co., wasadded to the mixture as a uniform suspension having a viscosity of18,000 cps. The circuit was mounted on the PC board as in the firstembodiment. 4 pounds of pressure was applied to the circuit for 5minutes under UV-light by a Blak-ray, longwave UV lamp. Mode B-100A madeby Ultra-Violet Product, Inc., San Gabriel, CA. The adhesive providedexcellent conductivity in the vertical direction and excellent lateralinsulation.

In another formulation, a mixture of 10 grams of Epic R1003, modifiedepoxy resin sold by Epic Resins, a division of RTE Corporation, 1900East North Street, Waukesha, Wis. 53186 and 5 grams of EPC H5002,modified aliphatic amine as hardener, also sold by Epic Resins, at roomtemperature, was added in varying amounts of 99.8% Nickel powder (lessthan 0.8 u by Fisher subsieve), sold by Aldrich Chemical Co., 940 WestSaint Paul Ave., Milwaukee, Wis. 53233. The mixture was mixed well untiluniform.

This epoxy resin and nickel powder mixture was uniformly coated on a PCboard, sold by 3M. The thickness is about 20 um after heating 150° C.for 15 minutes while applying pressure. Conductivity from terminal tosubstrate was then determined. The results are shown in Table I.

                  TABLE I                                                         ______________________________________                                        Amount of                                                                     Nickel Powder      Conductivity                                               (Percent by weight)                                                                              (ohm)                                                      ______________________________________                                        20                 >10.sup.14                                                 25                 >10.sup.14                                                 30                 >10.sup.14                                                 35                 >10.sup.13 (4.3 × 10.sup.13)                         40                 1.8 × 10.sup.6                                       45                 3.7 × 10.sup.-1                                      50                 1.26 × 10.sup.-3                                     55                 <10.sup.-3                                                 60                 <10.sup.-3                                                 ______________________________________                                    

The same procedure as set forth previously was utilized to make and testthe adhesive except that the digital integrated circuit was pressed withvarying pressure. The adhesive was cured at 150° C. for 15 minutes. Atthat time, the distance between the PC board and digital integratedcircuit were determined and conductivity between the conductive terminaland substrate was measured. The results are shown in Table II.

                  TABLE II                                                        ______________________________________                                        Applied   Distance Between                                                    Pressure  PC Board/         Conductivity                                      (PSI)     IC (um)           (ohm)                                             ______________________________________                                        0         38                >10.sup.14                                        0.5       36                >10.sup.14                                        1         31                2.7 × 10.sup.3                              3         28                4.3 × 10.sup.-1                             3.5       26                1.8 × 10.sup.-2                             4         23                1.1 × 10.sup.-3                             6         21                <10.sup.-3                                        10        16                <10.sup.-3                                        20        13                <10.sup.-3                                        40        12                <10.sup.-3                                        ______________________________________                                    

The aforementioned formulation show that there is effective insulationresistance between laterally spaced terminal members and conductivepaths (FIG. 4) while there is excellent conductivity between alignedterminal members and conductive paths (FIG. 5). Such conductivity andinsulation is exhibited over a wide range of voltages showing theinstant invention to be applicable in various environments and forvarious uses. Table I illustrates the relationship between metal powdercontent and conductivity, showing good conductivity beginning at aboutforty percent metal content. Table II illustrates varying amounts ofapplied pressure as well as preferred distances between terminal andsubstrate to provide good conductivity.

The invention has been described in an illustrative manner, and it is tobe understood that the terminology which has been used is intended to bein the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:
 1. A method of connecting a circuit member (18)having a plurality of laterally spaced conductive terminals (20) to asubstrate (12) including a mounting surface (14) having a plurality oflaterally spaced conductive paths (16), said method including the stepsof: applying an adhesive (22) including a resin having a viscosity of10,000 to 40,000 cps and having a twenty to twenty-five percent byweight content of spaced conductive metal particles suspended thereinover the mounting surface (14) of the substrate (12) having theconductive paths (16) wherein the resin is a dielectric preventingconductivity between the spaced metal particles therein; mounting thecircuit member (18) on the adhesive (22) while vertically aligning theconductive terminals (20) over preselected ones of the conductive paths(16); and characterized by applying pressure against the terminal (20)and the vertically aligned conductive path (16) and flowing the resinout from between the terminal (20) and conductive path (16) at a fasterrate than the conductive metal particles to concentrate the percent byweight content of the conductive metal particles in the resin betweeneach conductive terminal (20) and the vertically aligned conductive path(16) to between forty to fifty percent by weight and to decrease thespacing between the metal particles allowing conducting through theresin and making the resin uniaxially conductive vertically between theconductive terminal (20) and conductor path (16) while maintaining theadhesive (22) between laterally spaced terminals (20) and conductivepaths (16) in the unconcentrated and nonconductive state.
 2. A method asset forth in claim 1 wherein said step of applying pressure is furtherdefined as applying an ounce to 40 pounds per square inch of pressure.3. A method as set forth in claim 1 wherein said concentrating step isfurther defined as moving said conductive terminal (20) to within 20microns or less or less of said substrate (14).
 4. A method as set forthin claim 1 wherein the terminal members (20) are substantially rigidpins (20) extending from the circuit member (18), said concentratingstep being further defined as applying pressure on the circuit member(18) and forcing the rigid pins (20) against the substrate (12).
 5. Amethod as set forth in claim 1 wherein the terminal members (20) aresubstantially flexible, said concentrating step being further defined asapplying pressure directly on said flexible terminal members (20)against the substrate (12).
 6. A method as set forth in claim 1 furtherincluding the step of curing the adhesive (22) at a predetermined timeand temperature as the pressure is applied.
 7. A method as set forth inclaim 6 wherein said curing step is further defined as incubating theadhesive (22) at a temperature of 20° C. to 250° C. for 2 seconds to onehour.
 8. A method as set forth in claim 6 wherein said adhesive (22) isan ultraviolet curable adhesive, said curing step being further definedas irradiating said adhesive (22) under an ultraviolet cure lamp for apredetermined amount of time.
 9. A method as set forth in claim 1wherein said step of applying pressure is further defined as applyingthree to ten pounds of pressure.
 10. A method as set forth in claim 9wherein said step of applying pressure is further defined as applyingfour to five pounds of pressure.
 11. A method as set forth in claim 1including the step of preparing the adhesive by mixing the resin and ametal powder together to uniformly suspend the metal powder within theresin the mixture having a predetermined viscosity.
 12. A method as setforth in claim 1 wherein the viscosity of the adhesive mixture isbetween 15,000 and 20,000 cps.
 13. A method of securing two electricallyconductive members together, said method including the steps of:applying an adhesive including a resin having a viscosity of 10,000 to40,000 cps and having a twenty to twenty-five percent by weight contentof spaced conductive metal particles suspended therein between the twomembers wherein the resin is a dielectric preventing conductivitybetween the spaced metal particles, and forcing the members together andflowing the resin out from between the terminal (20) and conductive path(16) at a faster rate than the conductive metal particles to concentratethe percent by weight content of the metal particles in the resinbetween the members to between forty and fifty percent by weight todecrease the spacing between the metal particles allowing conductivitythrough the resin and making the resin conductive between the memberswhile maintaining the resin not between the members in theunconcentrated and nonconductive state.